The present invention relates to a liquid crystal display device, and more specifically, to improvements in visibility of a liquid crystal display device with a backlight for flashing the three primary colors of light: red, green and blue.
As a display device for displaying color images, there has been used a liquid crystal display device in which color display is generally performed by the combination of liquid crystal for switching light and a color filter containing the three primary colors of light: R, G, B. On the other hand, a liquid crystal display device with the three primary color sequential lighting system, which has a backlight for flashing the three primary colors of light: R, G, B and does not have any color filter, has been proposed in Japanese Unexamined Patent Publication No. 40260/1993. An example of structure of the liquid crystal display device with the three primary color sequential lighting system is shown in FIG. 9. The device is composed of a black-and-white liquid crystal display device without any color filter and a backlight which can emit the three primary colors of light: R, G, B independently. The timing chart indicating the operational principle of this liquid crystal display device is shown in FIG. 8. In FIG. 8, one display period indicates an update period of data to be displayed, and is usually set at 16.7 ms in ordinary liquid crystal display devices because the length of time does not make the human eye detect flicker. The backlight flashes light of e.g. red, green, and blue in this order, only one time for each color during one display period, and when one of these colors is exclusively displayed, the liquid crystal device is ON during the emission of the light source for the color, and becomes OFF during the display periods assigned to the other colors, thereby performing color display.
The display period for each color is generally set at 5.6 ms, which is ⅓ of 16.7 ms. In order to display a color other than the three primary colors, the liquid crystal device is made ON only during the periods for the colors necessary to reproduce the color. Making the liquid crystal device produce halftones which are between ON and OFF allows the three primary colors of light to be mixed in a desired ratio, thereby reproducing any desired color. In this display system, three different data for red, green, and blue are required to be displayed within a single display period. This causes an increase in display frequency; however, a color filter becomes unnecessary and color display is performed by a single pixel, which is advantageous to achieve higher precision in the display device.
In the conventional primary color sequential lighting system, the backlight for each color flashes light sequentially in a time-dividing manner. This makes the luminance of the backlight lower than those of the constant lighting type, which might cause problems on luminance in some uses. For example, when a liquid crystal display device with the three primary color sequential lighting system is used outdoors, the display might become illegible if ambient light such as sunshine is stronger than the backlight. There are other cases where the display does not produce desired light and shade when the liquid crystal becomes slow in response rate due to low temperatures.